The present invention relates to a conduit for supplying a fluid and damping pressure pulsations in the fluid, and particularly, though not exclusively, to a conduit for a vehicle power steering hydraulic circuit.
As is known, in hydraulic systems in which the operating fluid is circulated by a pump, the pressure pulsations generated by the pump are transmitted along the conduits and may give rise to undesired noise and vibration.
To reduce such pulsations, conduits are currently used in which the fluid is so routed as to produce reflected pressure waves which interfere with the incident waves; and, by appropriately sizing the lengths traveled by the waves, destructive wave interference, and hence a substantial reduction in pulsation, can be achieved at a given frequency.
In one known embodiment, conduits of the above type are defined by an outer pipe; and an inner pipe, which extends to an appropriately calculated length from an end fitting, and so defines an annular chamber with the outer pipe. The fluid flows along the fitting into the inner pipe and, at the outlet section of the inner pipe, the incoming pressure waves interfere with the waves traveling along the annular chamber and reflected by the end wall of the chamber defined by the fitting. For interference to be destructive, the length of the annular chamber must equal a quarter of the wavelength of the pressure waves.
Conduits of the above type are xe2x80x9ctunedxe2x80x9d by the above sizing of the inner pipe to a given frequency. In a real circuit, however, the pressure pulsations are periodic but not purely sinusoidal with a specific frequency, and can therefore be divided into a number of frequency components comprising a fundamental or first harmonic and harmonics of frequencies equal to multiples of the fundamental frequency. This therefore poses the problem of attenuating a number of components, typically the first two or three harmonics, which have a much greater amplitude than the higher-order harmonics. This can be done using a conduit comprising a number of elementary conduits of the above type arranged in series and each tuned to a respective frequency. Such a solution, however, is expensive and poses design limitations by imposing a minimum length of the conduit.
Patent EP 796408 describes a more compact solution (FIG. 1) wherein a conduit 1 comprises an outer pipe 2, and a first inner pipe 3 defining, with the outer pipe, an annular chamber 5 which comes out inside an expansion chamber 6 extending between first inner pipe 3 and a fitting 7 fixed inside an intermediate portion of outer pipe 2.
Fitting 7 is clamped inside outer pipe 2 by an outer sleeve 8 crimped onto outer pipe 2, and is fitted with one end of a second inner pipe 9 extending towards an outlet fitting 10 and defining with outer pipe 2 a second annular chamber 11, which is defined axially by fitting 7 and comes out at the opposite end inside a second expansion chamber 14 extending between second inner pipe 9 and outlet fitting 10. Second inner pipe 9 is closed at the free end by a plug 15 axially defining an inner chamber 18 of second inner pipe 9, and has at least one hole 17 connecting inner chamber 18 and second annular chamber 11 and located a predetermined distance from surface 13 of fitting 7 axially delimiting the second annular chamber 11.
Though technically effective, the above solution is relatively complex and expensive to produce by involving a large number of component parts and pipe cutting and assembly operations.
It is an object of the present invention to provide a fluid supply conduit designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a conduit for supplying a fluid and damping pressure pulsations in the fluid, and of the type comprising an outer pipe, two end fittings fixed in fluidtight manner to said outer pipe, and an inner pipe housed inside said outer pipe and forming therewith at least a first annular chamber; characterized in that one of said pipes comprises an intermediate portion deformed radially and cooperating in fluidtight manner, at least in use, with the other of said pipes.